Heat transfer medium



July 2, 1963 D. R. STERN ,095,

HEAT TRANSFER MEDIUM Filed Sept. 18, 1957 2 Sheets-Sheet 2 a B L 7 '10 aromefr/c 83 Energy Mixed Me7a/s 6 I Q M/xed Mefa/ EL M? I 1 "1'! i a u 1 E K -19 i E d l'i "2 I p a= 0. a E 18.0% Rb= 27.9% Rb 39.8%

Campos/#0115 1/7 Mo/ Per Cem INVENTOR. 2 David Aussefl Sfem AT ORNEYS W a I BY A MEMBER 0F 7'HE F/ United States Patent 3,095,698 HEAT TRANSFER MEDIUM David R. Stern, Fullerton, Califi, assignor to American Potash & Chemical Corporation, a corporation of Dela- Ware Filed Sept. 18, 1957, Ser. No. 684,719 2 Claims. (on. 60-36) This invention relates to heat transfer and particularly to a new and novel non-aqueous heat transfer composition having certain valuable properties.

There are many advantages in the use of a non-aqueous heat transfer composition and such materials as sodium, potassium, lithium, mercury, and various mixtures of these, have been proposed for utilization in power cycles. However, each of these suffers from a number of disadvantages which are absent from the composition of this invention. For example, they are either solids at ambient temperatures, have objectionable viscosities, or possess low thermal conductivity.

I have discovered that a composition of sodium, potassiurn and rubidium, in which the rubidium is the principal component, has many advantages over previously proposed heat transfer media. I have determined that the rubidium should comprise the major component, that sodium should be present in from about 16.1 percent to 49.8 percent, potassium from about 1.0 percent to 73.5 percent, with the balance rubidium.

In the drawings accompanying and forming a part hereof, FIGURE 1 is a phase diagram illustrating the compositions of this invention which are defined by the region ABCDLGFEHA.

FIGURE 2 is a graphic showing of the values along a plane through points H, I, J and K in FIGURE 1.

FIGURE 3 is a schematic apparatus and flow sheet for use with the composition.

In the following table, I have set forth pertinent thermodynamic data, comparing a typical mixed metal composition of this invention with the (thermodynamic properties of sodium, potassium, mercury and rubidium.

An examination of this data shows that the mixed metals of this invention have anextremely low melting point, 21 C., a high boiling point of 767 C., a high heat capacity, low viscosity and excellent thermoconductivity. Further, the materials have reasonable density.

Referring to FIGURE :1, attention is called to another aspect of my invention which is that I discovered, name- 3,095,698 Patented July 2, 1963 ice freezes at 21 C. and boils at 883, C., a 904 C.

range.

If one considers the usual ambient temperature to be 25 C., a mixed metal composition within this invention (point I), is liquid over a range 46 C. below the usual ambient temperature; since this is a physical mixture, the composition is a liquid over a 904 C. range, from -21 C. to 883 C., the boiling point of pure sodium.

The mixed metal heat transfer composition can be typically utilized in a heat transfer cycle such as that set forth diagrammatically in the accompanying drawing, FIGURE 3. In this, a mixture of the metals is withdrawn through pipe 5 from a storage tank 6 and is transferred by a pump 7 to a fractionator 20 and a boiler, generally indicated at 8. The boiler is supplied by a suitable energy source, generally indicated at 9, e.g., a thermal or atomic source. The rubidium is vaporized from the mixture into the overhead fractionator 20. Under atmospheric pressure, the temperature of the rubidium vapor will be 696 C.

The enriched rubidium vapor may be superheated, as in the superheater 12. The heated vapor is then transferred to a suitable device for extracting heat from the rubidium vapor whereby work is accomplished, such as the turbine, generally indicated at 14. The cooled rubidium vapor issuing from the turbine is transferred from line 16 to an air condenser 17, and the condensed liquid rubidium is returned through barometric leg 18 to the mixed metals storage vessel 6. Rubidium lean mixed metal is withdrawn through line 19 and is also returned to the mixed metal tank 6; thus, the rubidium vapor can be utilized effectively as a heat source and yet one need not deal with pure rubidium as such.

I claim:

1. A method of heat transfer comprising heating a ternary mixture of sodium, potassium and rubidium to provide a stream of hot rubidium vapor and a liquid residue lean in rubidium, extracting energy from the rubidium vapor whereby the vapor is cooled, condensing the cooled rubidium vapor, and returning the condensed rubidium to said liquid residue to provide said mixture for reuse, said mixture having a percentage composition falling along the line connecting points I, I and K of the drawing.

2. A ternary heat transfer mixture of sodium, potassium and rubidium and of a. composition falling along the line I, J and K of the drawing.

References Cited in the file of this patent UNITED STATES PATENTS 427,399 Campbell May 6, 1890 1,922,509 Thurm Aug. 15, 1933 1,982,745 Koenemann Dec. 4, 1934 2,575,322 Case Nov. 20, 1951 2,692,234 Insinger Oct. 19, 1954 

1. A METHOD OF HEAT TRANSFER COMPRISING HEATING A TERNARY MIXTURE OF SODIUM, POTASSIUM AND RUBIDIUM TO PROVIDE A STREAM OF HOT RUBIDIUM VAPOR AND A LIQUID RESIDUE LEAN IN RUBIDIUM, EXTRACTING ENREGY FROM THE RUBIDIUM VAPOR WHEREBY THE VAPOR IS COOLED, CONDENSING THE COOLED RUBIDIUM VAPOR, AND RETURNING THE CONDENSED RUBIDIUM TO SAID LIQUID RESIDUE TO PROVIDE SAID MIXTURE FOR REUSE, SAID MIXTURE HAVING A PERCENTAGE COMPOSITION 